Ipod connection for 2004 GMC SIerra?

I am looking to buy a ipod integration or ipod interface for a 2004 GMC Sierra that still has the factory radio (I want to keep the factory radio). It has XM capabilities, an AUX button and a Band/source button. I am looking to install it myself, just not sure which product to buy. I would like to control everything with my radio controls (integration) but am also concerned with price. Any suggestions as to what I need to get? Thanks! What are the more reliable/reptuable products?